Analysis of nucleic acid structure has become the focus of much of modem biology, biotechnology and medicine. Modem nucleic acid analysis techniques such as PCR, fragment-length-polymorphism analysis, and DNA sequencing provide information useful for a variety of applications including diagnosis of disease, organism identification, and tracking evolutionary relatedness. A necessary preliminary step in any nucleic acid analysis method is the preparation of nucleic acid which is free from contaminants which can interfere with enzymes used in these techniques, e.g., contaminants which can inactivate polymerase enzymes used in PCR and DNA sequencing methods.
A wide variety of nucleic acid purification techniques are available based on a range of different physical and chemical principles. The most common nucleic acid purification methods include organic/aqueous liquid--liquid extraction, solid-phase adsorption, precipitation, density-gradient centrifugation, and preparative electrophoresis. Electrophoretic methods are particularly attractive because they result in nucleic acid having a high purity and a large molecular weight.
But, conventional preparative electrophoretic methods suffer from significant shortcomings which limit their practical utility, particularly in the context of high-throughput applications. A particularly problematic aspect of conventional preparative electrophoretic methods is the manner in which a purified nucleic acid is removed from an electrophoresis medium, e.g., an electrophoresis gel. In one class of sample removal processes, the purified nucleic acid is manually excised from the electrophoresis gel. These sample-excision methods are disadvantageous because the nucleic acid and gel material must be separated after excision of the sample band, the procedure requires significant manual intervention, and the purified nucleic acid must be visualized prior to excision in order to locate the desired sample band. In a second class of sample removal techniques, the purified sample is eluted off of the electrophoresis gel into a gel-free buffer. However, such elution methods require that multiple fractions be collected, the purified sample band be visualized, and/or the elution properties of the desired nucleic acid be known.